We used our mail forwarding service physical address to establish residency in Florida. We then declared Florida as our domicile. Remember residency and domicile are different. Domicile is where your official address is for driver's license, vehicle registration, voter registration, etc. Residence is where you are presently living. Our domicile is Florida. In a couple of months our residence will be a SP in Colorado, but our domicile remains as Florida.
To enable you to get a Florida driver's license, you must have a legal residence (physical address) in Florida. Our mail forwarding service provides this. Once you get your Florida Driver's License, you can then register your vehicles in Florida, but you do not really have to. Remember the first time you register a vehicle in Florida the tag fees are high ($225 per tag plus the first year registration fee) but the renewals are about $70 or so. You should register to vote in the state you declare as your domicile. You also should file a notarized Declaration of Domicile form in the county where you have set up your physical address with the county clerk.
Our mail forwarding service (St. Brendan's Isle in Green Cove Springs, Florida) had all the instructions and necessary forms on their web site.